Children with specific language impairment (SLI) have interesting and unexplained deficits in their acquisition of grammatical morphemes. It is the purpose of the proposed project to explore the nature of this grammatical deficit and how it may interact with other components of the grammar. The proposed studies are designed to identify particular morphosyntactic deficits characteristic of SLI children. The specific aims are to evaluate predictions drawn from two new hypotheses, Extended Optionality and Missing Constraints. The hypotheses are drawn from current linguistic models of morphosyntax and normal children's acquisition patterns. Targeted grammatical features are tense, agreement, case, copula/auxiliary, and determiners. The work will proceed in two paths. Path 1 will consist of analyses of an existing transcript database containing spontaneous language samples from 101 5- year-old SLI children, 104 language-matched normal controls (a mean age of 36 months), and 21 normal age-matched controls. Path 2 will consist of an experi-longitudinal study, in which experimental grammatical probes will be collected from 20 4-year-old SLI children and equal numbers of language-matched and age-matched controls. Spontaneous language samples will also be collected. These children will be followed for 4 years, for a total of seven measurement times. The predictions will be tested in interrelated cross-sectional and longitudinal analyses. The findings would be relevant for clinical identification of SLI individuals, for the development of sensitive assessment batteries, and for the design of effective intervention techniques. A further outcome will be compilation of an archival database on SLI children and their normal control groups, which would be a scientific resource available to other investigators.